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SAN JOSE — A pair of earthquakes rattled the South Bay Tuesday night, in an area notorious for seismic restlessness, according to the U.S. Geological Survey.
A 3.9 magnitude quake, the stronger of the two temblors, struck at 10:32 p.m. about 5 miles east-northeast of Alum Rock at a depth of about 5.6 miles, the USGS reported.
The smaller quake — a 3.1 — hit at 7:19 p.m. about 5.6 miles east-northeast of San Martin at a depth of about 4.4 miles, the USGS said.
There were no immediate reports of injuries or damage.
Dave Freund of Los Gatos felt “a quick, small jolt on Lexington Reservoir.”
“A good shaker,” said Sanjay Khandelwal of Los Gatos. “My daughter felt it as well. She sleeps in a bunk bed and felt it move.”
The twin jolts were the latest in a series of sporadic tremors triggered by the Calaveras Fault, which routinely releases stress caused by the Earth’s shifting continental plates.
Last October, a 4.1 temblor struck in the same region. According to the USGS, it is not unusual for the Calaveras Fault to have magnitude 4 quakes, which are unlikely to cause structural damage to buildings.
The USGS estimates a 7.4 percent likelihood of a 6.7 magnitude or greater earthquake on the Calaveras Fault in the next 30 years, and a 14.3 percent chance on the Hayward Fault.
The Calaveras and Hayward faults are believed to be linked, which means that both could someday rupture together, resulting in a significantly more destructive earthquake than previously thought.
